1. Field of the Invention
The present invention relates to an SOI wafer and a method of manufacturing the same.
2. Description of the Background Art
As a method of manufacturing an SOI (Semiconductor on Insulator) wafer including a cavity pattern therein, there is known a bonding technique in which two silicon substrates are bonded to each other (for example, see Japanese Patent Application Laid-Open No. 2004-146461). Japanese Patent Application Laid-Open No. 2004-146461 describes a method of bonding a support substrate having a cavity pattern and an insulating layer formed thereon to an active semiconductor layer substrate for forming a device with the cavity pattern and the insulating layer being interposed therebetween. Moreover, there is known an SOI wafer in which a portion having an insulating layer and a portion having no insulating layer are provided as a predetermined pattern in the SOI wafer (see Japanese Patent Application Laid-Open No. 2004-228206).
When carrying out an exposure over an SOI wafer having a pattern formed therein as described above, it is necessary to perform the exposure by aligning the position of the pattern in the wafer and the position of an exposure mask with each other. However, an active semiconductor layer on a front surface of the wafer usually has a thickness of approximately 10 μm. Therefore, the pattern in the wafer is intercepted by the active semiconductor layer. Accordingly, the position of the pattern in the wafer cannot be detected by an image recognition with use of a detector provided in an exposing device. For this reason, an ordinary exposing device, more specifically, an exposing device for detecting a pattern on a front surface of a wafer to carry out an alignment of an exposure mask, cannot be compatible with an SOI wafer having a pattern in the wafer.
For this reason, in the background art, a superposition mark pattern for specifying the position of the pattern in the wafer is formed on a back surface of the SOI wafer having a pattern therein, and the pattern is detected by a special exposing device having a back surface detection, in order to align the exposure mask and the SOI wafer with each other by a method of indirectly recognizing the position of the pattern in the wafer.
Description will be given to the special exposing device having the back surface detection. A wafer stage holding the wafer has a hole penetrating therethrough. A superposition mark pattern is formed in such a manner that the superposition mark pattern on the back surface of the wafer is positioned in the hole, and the wafer is disposed in an optimum position on the wafer stage. By a detector disposed on the back side of the wafer stage, the position of the superposition mark pattern is detected via the hole penetrating through the wafer stage by means of a camera of the detector, for example. By a control unit provided in the exposing device, the position of the superposition mark pattern thus detected is analyzed to specify the position of the pattern in the wafer. Information on the position is sent to a mask stage holding the exposure mask, and the mask stage is moved to an optimum position on the wafer to carry out the exposure.
As described above, in the background art, in the case in which the exposure is carried out over the front surface of the SOI wafer having the pattern in the wafer, the superposition mark pattern for specifying the position of the pattern in the wafer is formed on the back surface of the SOI wafer, and furthermore, the special exposing device having the back surface detection is used to expose the SOI wafer in order to detect the pattern on the back surface.
In the SOI wafer including the pattern therein according to the background art, the pattern for specifying the position of the pattern in the wafer is to be formed on the back surface of the wafer. Consequently, a manufacturing process is complicated. For this reason, there is a problem in that a manufacturing cost is increased. In the case in which the SOI wafer is exposed, there is another problem in that it is necessary to use the special exposing device having the back surface detection and an equipment cost is also increased.